a. FIELD OF THE INVENTION
The present invention relates to a chloride ion-selective electrode, and particularly to a liquid film type, chloride ion-selective electrode based on a polymer support film suitable for measuring a chloride ion in body liquids.
b. RELATED ART STATEMENT
It is known to use, a chloride ion-selective electrode for measuring a chloride ion in body liquids, having a solid film type electrode comprising silver chloride and silver sulfide or a liquid film type electrode comprising a sensitive film which contains an ion exchange substance as a sensitive substance in a synthesized polymer support of polyvinyl chloride, etc. The former solid film type electrode is undesirably susceptible to influences by other halogen ions such as bromide ions and also by sulfide ions.
Japanese Patent Kokai (Laid-open) No. 57-77952 (1982) discloses a liquid film type electrode comprising a sensitive film containing a polymer resin as a support film material, methyltridecylammonium chloride as a sensitive substance, and n-tetradecyl alcohol as a plasticizer. U.S. Pat. No. 4,519,891 discloses a liquid film type electrode comprising a sensitive film containing a polyvinyl chloride as a support film material, dimethyldioctadecylammonium chloride as a sensitive substance, and a combination of n-tetradecyl alcohol and o-nitrophenyloctylether as a plasticizer. Microcimica Acta, [Wein], 1984, III, 1-16, describes a liquid film type electrode comprising a sensitive film containing a vinyl chloride polymer resin as a support film material, tetradodecylammonium chloride as a sensitive substance, and dioctyl sebacate as a plasticizer.
These known liquid film type electrodes have large error of measurement due to influences by substances such as lipophilic ions which are apt to be deposited on the surface of the sensitive film, and that the effective life of the electrode is rather short due to a leaching or dissolution of the sensitive substance i.e. ion exchange substance from the sensitive film into the liquid phase and also due to a deposition or adsorption of proteins and the like onto the surface of the sensitive film.
Furthermore, in the case of the known liquid type electrodes supported on a polymer resin, the selectivity over hydrophilic anions such as bicarbonate ions is decreased with a decrease of the selectivity over lipophilic anions, and the selectivity over the lipophilic anions is considerably decreased by enhancing the selectivity over hydrophilic anions such as bicarbonate ions. It is therefore important to enhance the selectivity over both hydrophilic anions and lipophilic anions, in order to decrease measurement errors and to improve measurement accuracy.
When the known liquid film type, chloride ion-selective electrodes supported on a polymeric material are employed for measuring chloride ions in blood, it is observed that the selectivity over lipophilic anions and hydrophilic anions is not satisfactorily high, so that these electrodes lack sufficient accuracy. Furthermore, the known liquid film type, chloride ion-selective electrodes based on a polymer support film do not prevent a leaching or dissolution of the sensitive substance from the support film, so that the electrodes have a relatively short effective life.